Preliminary studies in 39 patients showed that a new radioisotopic test of gallbladder function correctly identified all 10 patients with acute cholecystitis. The primary purpose of the present study is an extensive clinical evaluation of a new radiolabeled bile salt analog 99mTc-dihydrothiocitic acid (DHT) in patients presenting with abdominal complaints suggestive of acute cholecystitis. U45 of cholecystokinin will be given and 30 minutes later 2 mCi of 99mTc-DHT. Serial gamma camera images of the liver and gallbladder will be recorded.